Storage system and method of configuring the storage system

ABSTRACT

When storage controllers are added to a storage system to change the storage system from a configuration having only one storage controller to a configuration having plural storage controllers, or when storage controllers are removed from the storage system to change the storage system from a configuration having plural storage controllers to a configuration having only one storage controller, a controller-internal management-information memory controller carries out a copy process to copy management information from each of the storage controllers to a management-information-memory switch or vice versa at the same time as processing of read and write requests for access to the management information, made by a channel interface or a disc interface, in order to change storage locations of the management information while processing the read and write requests made by the host.

BACKGROUND OF THE INVENTION

1. Field of the Invention

In general, the present invention relates to a storage system and amethod of configuring the storage system. More particularly, the presentinvention relates to a storage system suitable for executing centralizedmanagement of management information of the storage system, which iscapable of continuing its operation, that is, without halting theoperation, when changing the storage system's configuration comprisingone storage controller or a plurality of storage controllers withoutregard to the configuration, and relates to a method of configuring thestorage system.

2. Description of the Related Art

There are a variety of storage systems, from a large-scale storagesystem demanded by typically a data center of an enterprise to asmall-scale storage system demanded by the general open market. Ineither case, performance and a storage capacity required of a small orlarge-scale storage system greatly vary in accordance with theapplication.

In order to solve a problem of scalability required of a storage system,there has been proposed a conventional method whereby a switch isprovided between a host computer and a storage system so as to allow anadditional storage system to be connected to the host computer byconnecting the switch by using a transfer path used in connecting thestorage systems to the host computer.

Also in order to solve a problem of scalability required of a storagesystem, there has been conceived another method whereby a plurality ofcomponents are connected to each other to form a multi-component storagesystem which appears to a host computer as a single storage system. Inaccordance with this method, data transfer paths andmanagement-information transfer paths inside the multi-component storagesystem are typically connected to each other to integrate the componentsinto a single storage system.

On the other hand, a micro program of a conventional storage system iswritten by assuming that the storage system serving as a control objectboth logically and physically has a structure of a single storagesystem. Thus, with a plurality of small-size storage systems connectedto each other to form a single storage system, if all the storagesystems are not regarded logically as a single storage system, it isnecessary to revise the conventional micro program's basic recognitionof the storage system. In this case, a modification range involves theentire micro program and the scale of the modification becomes extremelylarge.

Thus, also when a plurality of components are connected to each other toform a single storage system, there is raised a demand to regard thestructure of the connected components logically as the structure of thesingle storage system so that the micro program can be applied in adiversionary way.

If the structure of storage-system components is regarded logically asthe structure of a single storage system, management information of thesingle storage system is information of integrity, that is, informationthat cannot be separated into portions of the storage-system componentsas is the case with the management information of the conventionalstorage system. For this reason, in order to store the managementinformation, it is necessary to allocate a logically contiguous memoryarea as is the case with the conventional storage system.

As one of methods to allocate a memory area for storing managementinformation, management-information memories distributed amongstorage-system components are used. If physically distributedmanagement-information memories are to be managed logically as amanagement-information memory, however, a maintenance function becomesdifficult to implement. This is because, in the conventional storagesystem, management information is stored in a physically singlemanagement-information memory.

Assume that a plurality of components or small-size storage systems areconnected to each other to form a single storage system and, in thestate in which the connected components appear as a single storagesystem, any arbitrary small-size storage system is removed. In thiscase, an area for storing a part of management area is also removed aswell. Since the management information is information of integrity whichcannot be separated into portions, the management information becomesunusable even if only a part thereof is lost. Thus, if any arbitrarysmall-size storage system is removed, it is necessary to halt theoperation of the storage system.

By the way, members other than management-information memories each usedfor storing management information are also distributed among small-sizestorage systems. In implementation of a maintenance function for suchmembers, the conventional maintenance method can be adopted in adiversionary way relatively with ease. This is because, the conventionalstorage system also has functions to partially block, maintain andrecover configuration elements other than the management-informationmemories.

As described above, the conventional technology provides a methodwhereby a plurality of components or small-sized storage systems areconnected to each other to form a single storage system. However, thismethod has the following problems.

In the method whereby a plurality of components or small-sized storagesystems are connected to each other to form a single storage system, atechnique to manage all the small-sized storage systems is not takeninto consideration.

Thus, an attempt made to apply the micro program of the conventionalstorage system raises a problem that the scale to modify the microprogram becomes extremely large and the diversionary application of themicro program becomes difficult.

In addition, the method whereby a plurality of components or small-sizedstorage systems are connected to each other to form a single storagesystem does not consider a technique to store the storage system'smanagement information of integrity that cannot be separated intoportions of the small-size storage systems in management of thesmall-sized storage systems as a logically single storage system.

Thus, management information is stored in management-informationmemories employed in the physically distributed small-size storagesystems, making the maintenance function difficult to implement. Inaddition, there is also raised a problem that, since the managementinformation is also physically distributed, performance to make accessesto management information deteriorates as well.

Furthermore, in the conventional technology, a flexible technique ofcoping with changes in storage-system configuration is not taken intoconsideration either.

For example, when the storage-system configuration is changed from aconfiguration comprising a component of a storage system to aconfiguration comprising a plurality of components composing the storagesystem, making it necessary to transfer management information from onelocation to another, the operation of the storage system must be halted,raising a problem that a host is not capable of making an access to adisc storage in the mean time. This problem becomes serious inparticular in a version-up process of a large-scale storage system whichmust be operated all the time.

BRIEF SUMMARY OF THE INVENTION

It is thus an object of the present invention addressing the problemsdescribed above to provide a storage system that:

allows the configuration thereof to be changed with ease;

can be logically managed as a single storage system even if the singlestorage system is formed by connecting a plurality of components orsmall-sized storage systems to each other;

selects a storage location of management information in accordance withthe configuration of the storage system so as to implement centralizedmanagement of management information without regard to the configurationof the storage system; and

does not allow performance to make accesses to management information todeteriorate.

It is another object of the present invention to provide a method ofconfiguring a storage system that allows the configuration thereof to bechanged without halting the operation of the storage system so as toallow a host to make an access to a disc storage while the configurationis being changed.

In order to achieve one of the objects described above, in accordancewith the present invention's aspect related to a storage system, thereis provided a storage system allowing a host computer to make accessesto storages and comprising one or more storage controllers and thestorages wherein:

each of the storage controllers includes:

a channel interface connected to the host computer;

an interface connected to the storages; and

a management-information memory for storing management information ofthe storage system;

if the storage system includes a plurality of the storage controllers,the management-information memories employed in the storage controllersare connected to each other by a management-information-memory switchhaving a switch-internal management-information memory module;

if the storage system includes only one storage controller, themanagement-information memory of the storage controller has acontroller-internal management-information memory controller and acontroller-internal management-information memory module;

if the storage system includes a plurality of the storage controllers,the management-information memories employed in the storage controllerseach have the controller-internal management-information memorycontroller;

if the storage system includes only one storage controller, thecontroller-internal management-information memory controller makes anaccess to the controller-internal management-information memory moduleinside the storage controller; and

if the storage system includes a plurality of the storage controllers,the controller-internal management-information memory controllers makeaccesses to the switch-internal management-information memory moduleinside the management-information-memory switch.

To put it in more detail, if the storage system includes only onestorage controller, management information is stored in thecontroller-internal management-information memory module inside thestorage controller. If the storage system includes a plurality of thestorage controllers, on the other hand, management information is storedin the switch-internal management-information memory module inside themanagement-information-memory switch.

In order to achieve the other object described above, in accordance withthe present invention's other aspect related to a method of configuringa storage system, there is provided a method of configuring a storagesystem allowing a host computer to make accesses to storages andcomprising one or more storage controllers and the storages wherein:

each of the storage controllers includes:

a channel interface connected to the host computer;

an interface connected to the storages; and

a management-information memory for storing management information ofthe storage system;

if the storage system includes only one of the storage controllers, themanagement-information memory of the storage controller has acontroller-internal management-information memory controller and acontroller-internal management-information memory module; and

if the storage system includes a plurality of the storage controllers,the management-information memories employed in the storage controllersare connected to each other by a management-information-memory switchhaving a switch-internal management-information memory module and themanagement-information memories employed in the storage controllers eachhave the controller-internal management-information memory controller.

To put it in more detail, if the storage system includes only one of thestorage controller, management information is stored in thecontroller-internal management-information memory module inside thestorage controller. If the storage system includes a plurality of thestorage controllers, on the other hand, management information is storedin the switch-internal management-information memory module inside themanagement-information-memory switch.

In order to achieve the other object described above, in accordance withthe present invention's other aspect related to the method ofconfiguring a storage system wherein the management-information memoriesemployed in each of the additional storage controllers and themanagement-information-memory switches consist ofduplicated-management-information-storing systems, there is provided themethod's configuration for installing an additional one of the storagecontrollers whereby, when some of the storage controllers are newlyinstalled in addition to only one of the storage controller alreadyexisting in the storage system:

the management-information-memory switches are newly added forconnecting the management-information memories employed in the storagecontrollers to each other;

for each of the duplicated-management-information-storing systems, themanagement-information memory is connected to themanagement-information-memory switch;

to change stored locations of management information from themanagement-information memories of the storage controller alreadyexisting in said storage system to the management-information-memoryswitches, the duplicated-management-information-storing systems aresequentially subjected one system after another to a procedurecomprising the steps of:

blocking one of the duplicated-management-information-storing systems;

copying management information of the unblocked one of theduplicated-management-information-storing systems from themanagement-information memory to the management-information-memoryswitch of the blocked duplicated-management-information-storing system;and

de-blocking the blocked duplicated-management-information-storingsystem; and

the storage system carries out processing of an access made by the hostcomputer to the storages while the stored locations are being changed byusing management information stored in an unblocked one of theduplicated-management-information-storing systems.

In order to achieve the other object described above, in accordance withthe present invention's other aspect related to the method ofconfiguring a storage system wherein the management-information memoriesemployed in each of the additional storage controllers and themanagement-information-memory switches consist ofduplicated-management-information-storing systems, there is provided themethod's other configuration for removing any one of the storagecontrollers whereby, when some of the storage controllers are removedfrom the storage systems to leave only one of the storage controllers inthe storage system with the management-information memories connected tothe management-information-memory switch in all theduplicated-management-information-storing systems,

to change stored locations of management information from themanagement-information-memory switches to the management-informationmemories of the storage controller to leave alone in said storagesystem, the duplicated-management-information-storing systems aresequentially subjected one system after another to a procedurecomprising the steps of:

blocking any one of the duplicated-management-information-storingsystems;

copying management information of the unblocked one of theduplicated-management-information-storing systems from themanagement-information-memory switch to the management-informationmemory of the blocked duplicated-management-information-storing system;and

de-blocking the blocked duplicated-management-information-storingsystem, and

the storage system carries out processing of an access made by the hostcomputer to the storages while the stored locations are being changed byusing management information stored in an unblocked one of theduplicated-management-information-storing systems.

In order to achieve the other object described above, in accordance withthe present invention's other aspect related to the method ofconfiguring a storage system, there is provided the method's furtherconfiguration for installing an additional one of the storagecontrollers whereby, when some of the storage controllers are newlyinstalled in addition to only one of the storage controllers alreadyexisting in the storage system:

said management-information-memory switch is newly added for connectingsaid management-information memories employed in said storagecontrollers to each other; and

to change stored locations of management information from themanagement-information memory employed in the storage controller alreadyexisting in said storage system to the management-information-memoryswitches, management information stored in the management-informationmemory is copied to the management-information-memory switch in a copyoperation; and

the storage system carries out processing of an access made by the hostcomputer to the storages while the stored locations are being changed byusing management information stored in the management-information memoryemployed in the storage controllers each serving as a source of the copyoperation.

In order to achieve the other object described above, in accordance withthe present invention's other aspect related to the method ofconfiguring a storage system, there is provided the method's stillfurther configuration for removing any one of the storage controllerswhereby, when some of the storage controllers are removed from thestorage systems to leave only one of the storage controllers in thestorage system with the management-information memories connected to themanagement-information-memory switch:

to change stored locations of management information from themanagement-information-memory switch to themanagement-information-memory of the storage controller to leave alonein said storage system, management information stored in themanagement-information-memory switch is copied to themanagement-information memories in a copy operation; and

the storage system carries out processing of an access made by the hostcomputer to the storages while the stored locations are being changed byusing management information stored in the management-information-memoryswitch serving as a source of the copy operation.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF DRAWINGS

FIG. 1 is a diagram showing the configuration of a storage systemincluding only one storage controller as implemented by a firstembodiment of the present invention;

FIG. 2 is a diagram showing the configuration of a storage systemincluding a plurality of storage controllers as implemented by the firstembodiment of the present invention;

FIG. 3 is a flowchart representing a procedure for installing additionalstorage controllers 3 and additional disc storages 4 composing thestorage system 2 implemented by the first embodiment of the presentinvention;

FIG. 4 is a flowchart representing a procedure for removing storagecontrollers 3 and disc storages 4 composing the storage system 2implemented by the first embodiment of the present invention from thestorage system 2;

FIG. 5 is a flowchart representing a procedure for copying managementinformation when installing or removing storage controllers 3 and discstorages 4 in or from the storage system 2;

FIG. 6 is a flowchart representing a management-information copy process341 carried out in a channel interface 31;

FIG. 7 is a flowchart representing a procedure followed by the channelinterface 31 carrying out processing other than themanagement-information copy process 341 and a disc interface 35 formaking an access to management information;

FIGS. 8(a)-8(d) show a model representing flows of data in a process tocopy management information and an outline of the copy process in thefirst embodiment of the present invention wherein the managementinformation is copied from a management-information memory module 321employed in a storage controller 3 to a management-information memorymodule 62 employed in a management-information-memory switch 6;

FIGS. 9(a)-9(d) show a model representing flows of data in a process tocopy management information and an outline of the copy process in thefirst embodiment of the present invention wherein the managementinformation is copied from a management-information memory module 62employed in a management-information-memory switch 6 to amanagement-information memory module 321 employed in a storagecontroller 3;

FIG. 10 is a diagram showing the configuration of a storage systemincluding only one storage controller as implemented by a secondembodiment of the present invention;

FIG. 11 is a diagram showing the configuration of a storage systemincluding a plurality of storage controllers as implemented by thesecond embodiment of the present invention;

FIG. 12 is a flowchart representing a procedure for copying managementinformation when installing or removing storage controllers 3 and discstorages 4 in or from the storage system 2;

FIG. 13 is a flowchart representing a management-information copyfunction 346 carried out in the storage controller 3; and

FIG. 14 is a flowchart representing a procedure followed by the channelinterface 31 carrying out processing other than themanagement-information copy function 346 and a disc interface 35 formaking an access to management information;

PREFERRED EMBODIMENTS OF THE INVENTION

Preferred embodiments of the present invention are described byreferring to FIGS. 1 to 14 as follows.

First Embodiment

A first embodiment of the present invention is explained by referring toFIGS. 1 to 9.

(I): Configuration of the Storage System

First of all, the configuration of the storage system is explained byreferring to FIGS. 1 and 2. FIG. 1 is a diagram showing theconfiguration of a storage system 2 including only one storagecontroller 3 as implemented by a first embodiment of the presentinvention. On the other hand, FIG. 2 is a diagram showing theconfiguration of a storage system 2 including a plurality of storagecontrollers 3 as implemented by the first embodiment of the presentinvention.

The storage system 2 shown in FIG. 1 includes a storage controller 3connected to a host computer 1. The storage controller 3 is alsoconnected to a disc storage 4 and a service terminal 5. The disc storage4 is a hard disc having a large storage capacity. The service terminal 5is used by the user for entering a command to the storage controller 3and displaying internal status of the storage controller 3.

The storage controller 3 comprises a channel interface 31, a discinterface 35, a management-information memory 32 and a cache memory 33.Each member of the storage controller 3 is a duplicated-component membercomprising 2 identical components connected to each other by a path toincrease reliability.

The channel interface 31 is a member connected to the host computer 1whereas the disc interface 35 is a member connected to the disc storage4. The management-information memory 32 is a nonvolatile memory forstoring management information required for controlling the storagesystem 2.

The cache memory 33 is a memory for temporarily storing data in order toimprove performance of the host computer 1 in an operation to make anaccess to the disc storage 4.

The channel interface 31 carries out a management-information copyprocess 341 to copy management information from a normalmanagement-information memory 32 serving as one of the 2 identicalcomponents when the management-information memory 32 serving as theother identical component is undergoing a recovery process. Such amanagement-information copy process can also be carried out by the discinterface 35.

The management-information memory 32 comprises a controller-internalmanagement-information memory module 321 for storing managementinformation and a controller-internal management-information memorycontroller 322 for controlling the controller-internalmanagement-information memory module 321.

The controller-internal management-information memory module 321 is amemory module for storing management information of the storage system2.

The controller-internal management-information memory controller 322includes management-information-memory-controller status 342, acopied-management-information address 343 andmanagement-information-memory status 344.

The management-information-memory-controller status 342 is informationfor managing an access target in an operation to read out or writemanagement information. The management-information-memory status 344 isinformation on the status of the management-information memory 32. Thecopied-management-information address 343 is used for managing theprogress of the management-information copy process 341 to copymanagement information.

The cache memory 33 has a cache memory module 331 for storing data and acache memory controller 332 for controlling the cache memory module 331.

The storage system 2 shown in FIG. 2 includes a plurality of storagecontrollers 3, serving as an upgraded version of the storage system 2shown in FIG. 1. Each of the storage controllers 3 is also connected toa disc storage 4 and a service terminal 5.

The functions of members included in the configuration of the storagecontroller 3 are the same as those shown in FIG. 1. Each of the membersis also a duplicated-component member comprising 2 identical componentsconnected to each other by a path in the same way as the storage system2 shown in FIG. 1.

In the configuration including a plurality of storage controllers 3, acache-memory switch 7 and a management-information-memory switch 6 areprovided externally to the storage controllers 3. The cache-memoryswitch 7 is a switch for connecting the storage controller 3 to aselected one of the cache memories 33. By the same token, themanagement-information-memory switch 6 is a switch for connecting thestorage controller 3 to a selected one of the management-informationmemories 32.

The cache-memory switch 7 includes a cache-memory-switch controller 71connected to the cache-memory controller 332 employed in the cachememory 33 of the storage controller 3.

The management-information-memory switch 6 comprises amanagement-information-memory-switch controller 61, a switch-internalmanagement-information memory module 62 and a switch-internalmanagement-information-memory controller 63. Themanagement-information-memory-switch controller 61 is connected to thecontroller-internal management-information memory controller 322.

The switch-internal management-information memory module 62 is a memorymodule for storing management information.

The switch-internal management-information memory controller 63 is amember for controlling the switch-internal management-information memorymodule 62. The switch-internal management-information memory controller63 includes management-information-memory status 345. Themanagement-information-memory status 345 is status of managementinformation stored in the management-information-memory switch 6. Themanagement-information-memory status 345 is controlled so that themanagement-information-memory status 345 always matches themanagement-information-memory status 344 included in thecontroller-internal management-information memory controller 322employed in the storage controller 3.

The management-information memory 32 is a duplicated-component memorycomprising pairs each consisting of identical components. By the sametoken, the cache memory 33 is a duplicated-component memory comprisingpairs each consisting of identical components. For these reasons, inactuality, a pair of cache-memory switches 7 and a pair ofmanagement-information-memory switches 6 are required.

A relation between the configuration of the storage system 2 andimplementation members of management information is explained asfollows.

In the case of a storage system 2 comprising only one storage controller3, management information is stored in the controller-internalmanagement-information memory module 321 of the management-informationmemory 32 employed in the storage controller 3 shown in FIG. 1. In astorage system 2 comprising only one storage controller 3, neither themanagement-information-memory switch 6 nor the cache-memory switch 7 isrequired. By eliminating the management-information-memory switch 6 andthe cache-memory switch 7, the cost of the storage system 2 can bereduced.

In the case of a storage system 2 comprising a plurality of storagecontrollers 3, on the other hand, management information is stored inthe management-information memory module 62 employed in themanagement-information-memory switch 6 shown in FIG. 2 in order toassure performance of making an access to the management information.Thus, the management-information memory module 321 employed in each ofthe storage controllers 3 is not required.

(II): Procedure for Changing the Configuration of the Storage System

The following description explains a procedure for changing theconfiguration of the storage system 2 implemented by this embodiment byreferring to flowcharts shown in FIGS. 3 and 4.

FIG. 3 is a flowchart representing a procedure for installing additionalstorage controllers 3 and disc storages 4 in the storage system 2implemented by the first embodiment of the present invention. On theother hand, FIG. 4 is a flowchart representing a procedure for removingstorage controllers 3 and disc storages 4 from the storage system 2implemented by the first embodiment of the present invention. Thedescription begins with an explanation of the procedure for installingadditional storage controllers 3 and disc storages 4 in the storagesystem 2 with reference to the flowchart shown in FIG. 3.

The flowchart shown in FIG. 3 begins with a step S301 to determinewhether the storage system 2 includes only one storage controller 3. Ifthe storage system 2 includes more than one storage controller 3, theflow of the procedure goes on to a step S306. If the storage system 2includes only one storage controller 3, on the other hand, the flow ofthe procedure goes on to a step S302 at which amanagement-information-memory switch 6 and a cache-memory switch 7 areprepared and connected to the existing storage controller 3. Since amanagement-information-memory switch 6 and a cache-memory switch 7 arenot used so far, it is necessary to newly install them.

The flow of the procedure then goes on to a step S303 to determinewhether the management-information memory module 62 employed in themanagement-information-memory switch 6 has a storage capacity largeenough for accommodating management information stored in themanagement-information memory module 321 employed in the existingstorage controller 3. If the storage capacity is sufficient, the flow ofthe procedure goes on to a step S305.

If the storage capacity is not sufficient, on the other hand, the flowof the procedure goes on to a step S304 at which additionalmanagement-information memory modules 62 are installed in themanagement-information-memory switch 6 to provide a storage capacitylarge enough for accommodating management information stored in themanagement-information memory module 321 employed in the existingstorage controller 3.

Then, at the next step S305, management information is copied from themanagement-information memory module 321 employed in the storagecontroller 3 to the additional management-information memory modules 62employed in the management-information-memory switch 6. This copyprocess will be explained later by referring to flowcharts shown inFIGS. 5 and 6.

Subsequently, at the next step S306, an additionally installed discstorage 4 is connected to an additionally installed storage controller3, and the additionally installed storage controller 3 is connected tothe management-information-memory switch 6 and the cache-memory switch7.

The flow of the procedure then goes on to a step S307 to determinewhether the management-information-memory switch 6 has a storagecapacity large enough for the installed additional disc storage 4 andthe installed additional storage controller 3. If the storage capacityis large enough, the flow of the procedure goes on to a step S309. Ifthe storage capacity is not large enough, on the other hand, the flow ofthe procedure goes on to a step S308 at which additionalmanagement-information memory modules 62 are installed in themanagement-information-memory switch 6 to provide a storage capacitylarge enough for the installed additional disc storage 4 and theinstalled additional storage controller 3.

Then, at the next step S309, management information for using theadditionally installed disc storage 4 and the additionally installedstorage controller 3 is developed in the management-information memorymodule 62 employed in the management-information-memory switch 6.

Finally, at the last step S310, use of the additionally installed discstorage 4 and the additionally installed storage controller 3 isstarted.

The description continues to an explanation of the procedure forremoving storage controllers 3 and disc storages 4 from the storagesystem 2 with reference to the flowchart shown in FIG. 4. The flowchartshown in FIG. 4 begins with a step S401 to end use of a disc storage 4and a storage controller 3, which are to be removed.

Then, at the next step S402, management information required for usingthe disc storage 4 and the storage controller 3, which are to beremoved, is deleted from the management-information memory module 62employed in the management-information-memory switch 6. This procedureis executed in the same way as deletion of a storage, a channelinterface and a disc interface from the conventional storage system.

The flow of the procedure then goes on to a step S403 to determinewhether the management-information memory module 62 employed in themanagement-information-memory switch 6 has a memory no longer requireddue to the removal of the disc storage 4 and the storage controller 3.If the management-information memory module 62 employed in themanagement-information-memory switch 6 does not have such a memory, theflow of the procedure goes on to a step S405. If themanagement-information memory module 62 employed in themanagement-information-memory switch 6 includes such a memory, on theother hand, the flow of the procedure goes on to a step S404 to removemanagement-information memory modules 62, which constitute the memory nolonger required due to the removal of the disc storage 4 and the storagecontroller 3, from the management-information-memory switch 6.

Then, at the next step S405, the storage controller 3 to be removed isdisconnected from the management-information-memory switch 6 and thecache-memory switch 7. The flow of the procedure subsequently goes on toa step S406 to determine whether only one storage controller 3 remainsin the storage system 2 as a result of the removals. If more than onestorage controller 3 remains in the storage system 2 as a result of theremovals, the execution of the procedure is ended. If only one storagecontroller 3 remains in the storage system 2 as a result of theremovals, on the other hand, the flow of the procedure goes on to a stepS407 to determine whether the management-information memory module 321employed in the remaining storage controller 3 has a storage capacitylarge enough for accommodating management information stored in themanagement-information memory module 62 employed in themanagement-information-memory switch 6. This determination is requiredsince management information will be transferred from themanagement-information memory module 62 employed in themanagement-information-memory switch 6 to the management-informationmemory 32 employed in the remaining storage controller 3. If the storagecapacity is large enough, the flow of the procedure goes on to a stepS409. If the storage capacity is not large enough, on the other hand,the flow of the procedure goes on to a step S408 at which additionalmanagement-information memory modules 321 are installed in the storagecontroller 3 to provide a storage capacity large enough foraccommodating management information stored in themanagement-information memory module 62 employed in themanagement-information-memory switch 6.

Then, at the next step S409, management information is copied from themanagement-information memory module 62 employed in themanagement-information-memory switch 6 to management-information memorymodules 321 employed in the storage controller 3. This copy process willbe explained later by referring to flowcharts shown in FIGS. 5 and 6.

Finally, at the step S410, the remaining storage controller 3 isdisconnected from the management-information-memory switch 6 and thecache-memory switch 7.

(III): Details of the Management-Information Copy Process and Process toAccess Management Information

The following description explains a process 341 to copy managementinformation and a process to make an access to management information byreferring to flowcharts shown in FIGS. 5 to 7.

FIG. 5 is a flowchart representing a procedure for copying managementinformation when installing or removing storage controllers 3 and discstorages 4 in or from the storage system 2. FIG. 6 is a flowchartrepresenting a management-information copy process 341 carried out in achannel interface 31.

FIG. 7 is a flowchart representing a procedure followed by the channelinterface 31 carrying out processing other than themanagement-information copy process 341 and a disc interface 35 formaking an access to management information.

Before details of procedures related to management information areexplained, preparatory concepts and cautions are described.

In this embodiment, in order to assure reliability, each member of thestorage controller 3 is designed into a duplicated-componentconfiguration comprising 2 identical components. In order to keep upwith such duplicated-component configurations, themanagement-information-memory switch 6 and the cache-memory switch 7 areeach also designed into a duplicated-component configuration comprising2 identical components. Members of the storage controller 3 include thechannel interface 31, the disc interface 35, the management-informationmemory 32, the cache memory 33.

Thus, when management information is copied from themanagement-information memory 32 to the management-information-memoryswitch 6, for example, the copy process must be carried out from the 2identical components of the management-information memory 32 torespectively the 2 identical components of themanagement-information-memory switch 6. Thus, attention needs to be paidto the fact that, if management information in one of the 2 identicalcomponents of a member employed in the storage controller 3 cannot bereferenced while the same management information in the other componentcan be referenced, the operation of the storage controller 3 does nothave to be halted. A caution also needs to be exercised in a process tocopy management information since an operation to update the managementinformation during the copy process may cause data integrity to be lost.

Status of a management-information memory is defined for controlling aprocess to copy management information and other processing. Threedefined kinds of status are ‘Normal’, ‘Blocked’, and ‘Being copied’. TheNormal status means that management information stored in amanagement-information memory can be referenced and used. The Blockedstatus indicates that management information stored in amanagement-information memory cannot be referenced. The ‘Being-copied’status implies that management information stored in amanagement-information memory is being copied.

It should be noted that, while all management information is assumed tobe duplicated in the 2 identical memory components in this embodimentfor the sake of simplicity, a case in which not all managementinformation is duplicated is also included in the scope of the presentinvention. Management information, that cannot be referenced and updatedbut can be processed without halting the operation of the storagecontroller 3, does not have to be made an object of themanagement-information copy process 341. Control needs to be executed sothat, with the management-information-memory status 344 and themanagement-information-memory status 345 put in the Blocked status, suchmanagement information cannot be referenced or updated. Byreconstruction of such management information before themanagement-information-memory status 344 and themanagement-information-memory status 345 are set to Normal, however, thereconstructed management information can be referenced and updated afterthe management-information-memory status 344 and themanagement-information-memory status 345 have been set to Normal.

The management-information-memory status is applicable to both themanagement-information memory controller 322 employed in the storagecontroller 3 and the management-information memory controller 63employed in the management-information-memory switch 6. As describedabove, the controller-internal management-information memory controller322 and the switch-internal management-information memory controller 63each have a duplicated-component configuration comprising 2 identicalcomponents. It is necessary to establish in advance a rule requiringthat the controller-internal management-information memory controller322 serving as one of its 2 identical components shall always be put inthe same management-information-memory status as the switch-internalmanagement-information memory controller 63 serving as the one of its 2identical components. By the same token, the controller-internalmanagement-information memory controller 322 serving as the otheridentical component shall always be put in the samemanagement-information-memory status as the switch-internalmanagement-information memory controller 63 serving as the otheridentical component.

On the other hand, the management-information memory controller 322employed in the storage controller 3 also hasmanagement-information-memory-controller status 342 indicating thestorage location of management information to be accessed. Themanagement-information-memory-controller status 342 applies to both thecontroller-internal management-information memory controller 322 servingas one of its 2 identical components and the controller-internalmanagement-information memory controller 322 serving as its otheridentical component. The management-information-memory-controller status342 may have a value of ‘Accesses to management information in themanagement-information-memory switch’ indicating that thecontroller-internal management-information memory controller 322 shouldmake an access to management information in themanagement-information-memory switch 6. On the other hand, themanagement-information-memory-controller status 342 may also have avalue of ‘Accesses to management information in the storage controller’implying that the controller-internal management-information memorycontroller 322 should make an access to management information in thestorage controller 3.

A management-information copy process 341 is represented by a flowchartshown in FIG. 5. As shown in the figure, the flowchart begins with astep S501 at which the management-information-memory status 344 of thestorage controller 3 serving as one of its 2 identical components andthe management-information-memory status 345 of themanagement-information-memory switch 6 serving as one of its 2 identicalcomponents are put in the Block status from the service terminal 5.Thus, attention needs to be paid to the fact that themanagement-information-memory status 344 of the storage controller 3 andthe management-information-memory status 345 of themanagement-information-memory switch 6 serving have been put in theBlock status.

The Blocked status prevents the channel interface 31 and the discinterface 35 from referencing and updating management information.

Even if the management-information-memory status 344 of the storagecontroller 3 serving as one of its 2 identical components and themanagement-information-memory status 345 of themanagement-information-memory switch 6 serving as one of its 2 identicalcomponents are put in the Block status, the storage system 2 is capableof continuing its operation by using management information stored inthe management-information memory module 321 employed in the storagecontroller 3 serving as its other identical component or themanagement-information memory module 62 employed in themanagement-information-memory switch 6 serving as its other identicalcomponents.

The flow of the management-information copy procedure then goes on to astep S502 to determine whether the direction to copy managementinformation is from the storage controller 3 to themanagement-information-memory switch 6.

A direction to copy management information from the storage controller 3to the management-information-memory switch 6 indicates that storagecontrollers 3 are newly added to the storage system 2 so that thestorage system 2 is changed from a configuration with only one storagecontroller 3 to a configuration having a plurality of storagecontrollers 3. In this case, the management-information-memory switch 6is also newly added. On the contrary, a direction to copy managementinformation from the management-information-memory switch 6 to thestorage controller 3 indicates that storage controllers 3 are removedfrom the storage system 2 so that the storage system 2 is changed from aconfiguration having a plurality of storage controllers 3 to aconfiguration with only one storage controller 3. In this case, themanagement-information-memory switch 6 is also eliminated.

If the direction to copy management information is from the storagecontroller 3 to the management-information-memory switch 6, the flow ofthe management-information copy process goes on to a step S503 at whichthe management-information-memory-controller status 342 of thecontroller-internal management-information memory controller 322 in theblocked storage controller 3 is changed from ‘Accesses to managementinformation in the storage controller’ to ‘Accesses to managementinformation in the management-information-memory switch’ from theservice terminal 5. This is because themanagement-information-memory-controller status 342 will be referred tofor determining whether management information in thecontroller-internal management-information memory module 321 or theswitch-internal management-information memory module 62 is to bereferenced or updated after the management-information copy process 341is completed. By changing the value of themanagement-information-memory-controller status 342 in the blockedstorage controller 3 as described above, the controller-internalmanagement-information memory controller 322 of the storage controller 3will thereafter direct a request for an access to management informationto the management-information-memory switch 6.

If the direction to copy management information is from themanagement-information-memory switch 6 to the storage controller 3, onthe other hand, the flow of the management-information copy process goeson to a step S504 at which the management-information-memory-controllerstatus 342 of the controller-internal management-information memorycontroller 322 in the blocked storage controller 3 is changed from‘Accesses to management information in the management-information-memoryswitch’ to ‘Accesses to management information in the storagecontroller’ from the service terminal 5. As described above, themanagement-information-memory-controller status 342 will be referred tofor determining whether management information in thecontroller-internal management-information memory module 321 or theswitch-internal management-information memory module 62 is to bereferenced or updated after the management-information copy process 341is completed. By changing the value of themanagement-information-memory-controller status 342 in the blockedstorage controller 3 as described above, the controller-internalmanagement-information memory controller 322 of the storage controller 3will thereafter direct a request for an access to management informationto the storage controller 3.

Then, at the next step S505, the management-information-memory status344 of the blocked storage controller 3 and themanagement-information-memory status 345 of the blockedmanagement-information-memory switch 6 are put in Being-copied status,and management-information copy process 341 is started from the serviceterminal 5. Details of the management-information copy process 341 willbe described by referring to a flowchart shown in FIG. 6.

The flow of the management-information copy procedure then goes on to astep S506 to wait for the management-information copy process 341 to becompleted. Then, at the next step S507, themanagement-information-memory status 344 and themanagement-information-memory status 345, which were put in theBeing-copied status, are verify to have been restored to the Normalstatus.

At this point of time, management information has been copied from themanagement-information memory module 321 employed in the blocked storagecontroller 3 having a duplicated-component configuration to themanagement-information memory module 62 employed in the unblockedmanagement-information-memory switch 6 also having aduplicated-component configuration, or management information has beencopied from the management-information memory module 62 employed in theblocked management-information-memory switch 6 having aduplicated-component configuration to the management-information memorymodule 321 employed in the unblocked storage controller 3 also having aduplicated-component configuration.

Then, at the next step S508, the management-information-memory status344 of the storage controller 3 serving as the other identical componentand the management-information-memory status 345 of themanagement-information-memory switch 6 serving as the other identicalcomponent are put in the Block status. Subsequently, pieces ofprocessing are carried out at steps S509 to S514 in the same way as thesteps S502 to S507 respectively.

Finally, management information is all copied from theduplicated-component configuration of the controller-internalmanagement-information memory module 321 to the duplicated-componentconfiguration of the switch-internal management-information memorymodule 62, or management information is all copied from theduplicated-component configuration of the switch-internalmanagement-information memory module 62 to the duplicated-componentconfiguration of the controller-internal management-information memorymodule 321.

Next, a detailed procedure of the management-information copy process341 is explained by referring to a flowchart shown in FIG. 6. Themanagement-information copy process 341 is carried out at the steps S505and S512 of the flowchart shown in FIG. 5. In addition, themanagement-information copy process 341 is also carried out forrecovering the management-information memory 32.

The flowchart representing the management-information copy process 341begins with a step S601 at which the address 343 of copied managementinformation is to point to the beginning of a management-informationcopy destination. The flow of the procedure then goes on to a step S602to determine whether the address 343 of copied management informationhas reached the end of the management-information copy destination. Ifthe address 343 of copied management information has reached the end ofthe management-information copy destination, the flow of the proceduregoes on to a step S606 at which pieces of management-information memorystatus 344 and 345 are changed from ‘Being copied’ to ‘Normal’. Then,the management-information copy process 341 is ended.

If the address 343 of copied management information has not reached theend of the management-information copy destination, on the other hand,the flow of the procedure goes on to a step S603 at which managementinformation of a predetermined amount is read out from thecontroller-internal management-information memory module 321 in ‘Normal’management-information memory status 344 and written into theswitch-internal management-information memory module 62 in‘Being-copied’ management-information memory status 345, or read outfrom the switch-internal management-information memory module 62 in‘Normal’ management-information memory status 345 and written into thecontroller-internal management-information memory module 321 in‘Being-copied’ management-information memory status 344.

Then, at the next step S604, the address 343 of copied managementinformation is incremented by an increase corresponding to the amount ofcopied management information. Subsequently, at the next step S605, themanagement-information copy process 341 is suspended for a predeterminedperiod of time in order to reduce the degradation of performance toprocess a read or write request which is made by the host computer 1 inthe course of the management-information copy process 341. The flow ofthe procedure then goes back to the step S602.

The following description explains a procedure followed by the channelinterface 31 carrying out processing other than themanagement-information copy process 341 and a disc interface 35 formaking an access to management information by referring to a flowchartshown in FIG. 7

In this processing, it is important not to lose integrity of managementinformation being copied when updating management information.

As described above, attention needs to be paid to the fact that themanagement-information-memory-controller status 342 of thecontroller-internal management-information memory controller 322indicates whether management information in the controller-internalmanagement-information memory module 321 or management information inthe switch-internal management-information memory module 62 is to beaccessed. Thus, in the following description of the flowchart shown inFIG. 7, the management-information-memory status 344 also represents themanagement-information-memory status 345 and the management-informationmemory module represents either the controller-internalmanagement-information memory module 321 or the switch-internalmanagement-information memory module 62.

The flowchart begins with a step S701 at which themanagement-information-memory status 344 of the management-informationmemory module serving as one of the 2 identical components and themanagement-information-memory status 344 of the management-informationmemory module serving as the other identical component can bereferenced. The flow of the procedure then goes on to a step 702 todetermine whether the management-information-memory status 344 of themanagement-information memory module serving as one of the 2 identicalcomponents and the management-information-memory status 344 of themanagement-information memory module serving as the other identicalcomponent are normal.

If the management-information-memory status 344 of themanagement-information memory module serving as one of the 2 identicalcomponents and the management-information-memory status 344 of themanagement-information memory module serving as the other identicalcomponent are found normal, the flow of the procedure goes on to a stepS703 at which pieces of management information in both themanagement-information memory module serving as one of the 2 identicalcomponents and the management-information memory module serving as theother identical component are accessed.

If the management-information-memory status 344 of themanagement-information memory module serving as one of the 2 identicalcomponents and the management-information-memory status 344 of themanagement-information memory module serving as the other identicalcomponent are found not both normal, on the other hand, the flow of theprocedure goes on to a step S704 to determine whether themanagement-information-memory status 344 of non-normalmanagement-information memory module 321 is Being-copied.

If the management-information-memory status 344 of non-normalmanagement-information memory module 321 is not Being-copied, the flowof the procedure goes on to a step S705 at which management informationin the management-information memory module 321 in Normal status isaccessed. If the management-information-memory status 344 of non-normalmanagement-information memory module 321 is Being-copied, on the otherhand, the flow of the procedure goes on to a step S706 at which theaddress 343 of copied management information is referenced. Then, theflow of the procedure goes on to a step S707 to determine whether theaccess request is a write request and whether the address of the accesstarget lies ahead of the address 343 of copied management information.An address of the access target lying ahead of the address 343 of copiedmanagement information indicates that the access is an access to aregion for which a copy operation has already been completed. This isbecause a copy operation starts from a start address toward subsequentaddresses.

If at least the access request is not a write request or the address ofthe access target does not lie ahead of the address 343 of copiedmanagement information, the flow of the procedure goes on to the stepS705. Such an access request is a request to read out data or a requestto write data which, in this case, needs to be merely written into thecopy source only. If the access request is a write request and theaddress of the access target lies ahead of the address 343 of copiedmanagement information, on the other hand, the flow of the proceduregoes on to a step S708 at which management information is written intoboth the management-information memory modules serving as the copysource and the copy destination. The processing of the step S708 iscarried out in order to maintain integrity of duplicated pieces ofidentical management information at the end of themanagement-information copy process 341. That is, the write operation iscarried out also on the copy destination. The management information isthus written into a copy destination in the Being-copied status. Thecopy destination is also determined by the value of themanagement-information-memory-controller status 342

(IV): Data Flows of the Management-Information Copy Process and outlineof the Management-Information Copy Process

The following description explains data flows of themanagement-information copy process and an outline of themanagement-information copy process by referring to FIGS. 8 and 9.

FIG. 8 is a diagram showing a model representing flows of data in aprocess to copy management information and an outline of the copyprocess in the first embodiment of the present invention wherein themanagement information is copied from a management-information memorymodule 321 employed in a management-information memory 32 to amanagement-information memory module 62 employed in amanagement-information-memory switch 6.

On the other hand, FIG. 9 is a diagram showing a model representingflows of data in a process to copy management information and an outlineof the copy process in the first embodiment of the present inventionwherein the management information is copied from amanagement-information memory module 62 employed in amanagement-information-memory switch 6 to a management-informationmemory module 321 employed in a management-information memory 32.

The model shown in FIG. 8 represents a process to copy managementinformation from a management-information memory module 321 employed ina management-information memory 32 to a management-information memorymodule 62 employed in a management-information-memory switch 6. Such amanagement-information copy process is carried out when storagecontrollers 3 are newly installed in the storage system 2 to change thestorage system 2 from a configuration comprising one storage controller3 to a configuration comprising a plurality of storage controllers 3.When such storage controllers 3 are newly added, themanagement-information-memory switch 6 is also newly installed as well.

The management-information memory 32 shown on the upper side of each ofFIGS. 8(a) to 8(d) is a duplicated-component member comprising 2identical components represented by symbols A and B. By the same token,the management-information-memory switch 6 shown on the lower side ofeach of FIGS. 8(a) to 8(d) is a duplicated-component member comprising 2identical components represented by symbols A and B. As described above,the management-information memory 32 includes the controller-internalmanagement-information memory module 321 and themanagement-information-memory switch 6 has the switch-internalmanagement-information memory module 62 as shown in the figure. A phrasewritten beside the controller-internal management-information memorymodule 321 or the switch-internal management-information memory module62 in each of FIGS. 8(a) to 8(d) describes the management-informationmemory status 344 or 345 of the controller-internalmanagement-information memory module 321 or the switch-internalmanagement-information memory module 62. A phrase written outside boxesof each of FIGS. 8(a) to 8(d) describes the management-informationmemory controller status 342 of the storage controller 3.

Since FIG. 8 is a diagram showing flows of data and an outline ofprocessing, the figure does not show configuration elements other thanthe flows and the outline. In the following description, the phrase“management information is stored in the management-information memory32” or “management information is stored in the storage controller 3”means that the management information is stored in themanagement-information memory module 321 employed in themanagement-information memory 32 of the storage controller 3. By thesame token, the phrase “management information is stored in themanagement-information-memory switch 6” means that the managementinformation is stored in the management-information memory module 62employed in the management-information-memory switch 6. In addition, anA system comprises an A management-information memory 32 and an Amanagement-information memory switch 6. Likewise, a B system comprises aB management-information memory 32 and a B management-information memoryswitch 6.

To begin with, in an initial state shown in FIG. 8(a), pieces ofmanagement information of the A and B systems are both stored in the Aand B management-information memories 32 respectively. The A and Bmanagement-information memories 32 both have management-informationmemory status 344 of Normal. As described earlier, the Amanagement-information memory 32 and the A management-information memoryswitch 6 have the same management-information memory status, whereas theB management-information memory 32 and the B management-informationmemory switch 6 have the same management-information memory status. Inthe initial state, the A and B systems both have management-informationmemory controller status 342 of “Accesses to management information instorage controller.” With this status, the storage controller 3 makesaccesses to management information stored in the management-informationmemory 32.

In a management-information copy process 341, first of all, the A systemis put in a Blocked management-information memory status as shown inFIG. 8(b) at the step S501 of the flowchart shown in FIG. 5. With suchstatus, the storage controller 3 is no longer allowed to use managementinformation stored in the A system.

Then, the management-information memory controller status 342 of the Asystem is changed to “Accesses to management information in themanagement-information memory switch” at the step S503 of the flowchartshown in FIG. 5, and the management-information memory status of the Asystem is changed to “Being copied” before the management-informationcopy process is started at the step S505 of the flowchart shown in FIG.5. The copy source of the management-information copy process is the Bmanagement-information memory 32. This copy source agrees with theNormal management-information memory status of the B system and the“Accesses to management information in the management-information memoryswitch” management-information memory controller status 342 of the Bsystem. On the other hand, the copy destination of themanagement-information copy process is the A management-informationmemory switch 6. This copy destination agrees with the “Being copied”management-information memory status of the A system and results of themanagement-information copy process 341 will reflect the fact that themanagement-information memory controller status 342 of the A system hasbeen changed to “Accesses to management information in themanagement-information memory switch.” Thus, management information iscopied from the B management-information memory 32 to the Amanagement-information memory switch 6 at the step S603 of the flowchartshown in FIG. 6.

As the copy operation is completed, the management-information memorystatus of the A system is restored to “Normal” at the step S606 of theflowchart shown in FIG. 6 while the management-information memory statusof the B system is changed to “Blocked” at the step S508 of theflowchart shown in FIG. 5 as shown in FIG. 8(c).

Then, the management-information memory controller status 342 of the Bsystem is changed to “Accesses to management information in themanagement-information memory switch” at the step S510 of the flowchartshown in FIG. 5, and the management-information memory status of the Bsystem is changed to “Being copied” before a second copy operation isstarted at the step S512 of the flowchart shown in FIG. 5. The copysource of the second copy operation is the A management-informationmemory switch 6. This copy source agrees with the Normalmanagement-information memory status of the A system and the “Accessesto management information in the management-information memory switch”management-information memory controller status 342 of the A system. Onthe other hand, the copy destination of the management-information copyprocess is the B management-information memory switch 6. This copydestination agrees with the “Being copied” management-information memorystatus of the B system and results of the management-information copyprocess 341 will reflect the fact that the management-information memorycontroller status 342 of the B system has been changed to “Accesses tomanagement information in the management-information memory switch.”Thus, management information is copied from the A management-informationmemory switch 6 to the B management-information memory switch 6 at thestep S603 of the flowchart shown in FIG. 6.

As this second copy operation is completed, the management-informationmemory status of the B system is restored to “Normal” at the step S606of the flowchart shown in FIG. 6 as shown in FIG. 8(d). In the stateshown in FIG. 8(d), the storage controller 3 is capable of operating bymaking accesses to management information stored in themanagement-information memory switch 6 having a duplicated-componentconfiguration.

Next, the model shown in FIG. 9 represents a process to copy managementinformation from a management-information memory module 62 employed in amanagement-information-memory switch 6 to a management-informationmemory module 321 employed in a management-information memory 32. Such amanagement-information copy process is carried out when storagecontrollers 3 are removed from the storage system 2 to change thestorage system 2 from a configuration comprising a plurality of storagecontrollers 3 to a configuration comprising only one storage controller3. When storage controllers 3 are removed as such, themanagement-information-memory switch 6 is also removed as well.

To begin with, in an initial state shown in FIG. 9(a), pieces ofmanagement information of the A and B systems are both stored in the Aand B management-information memory switches 6 respectively. The A and Bmanagement-information memory switches 6 both havemanagement-information memory status 345 of Normal. As describedearlier, the A management-information memory 32 and the Amanagement-information memory switch 6 have the samemanagement-information memory status, whereas the Bmanagement-information memory 32 and the B management-information memoryswitch 6 have the same management-information memory status. In theinitial state, the A and B systems both have management-informationmemory controller status 342 of “Accesses to management information inthe management-information memory switch.” With this status, the storagecontroller 3 makes accesses to management information stored in themanagement-information memory switch 6.

In a management-information copy process 341, first of all, the A systemis put in a Blocked management-information memory status as shown inFIG. 9(b) at the step S501 of the flowchart shown in FIG. 5. With suchstatus, the storage controller 3 is no longer allowed to use managementinformation stored in the A system.

Then, the management-information memory controller status 342 of the Asystem is changed to “Accesses to management information in the storagecontroller” at the step S504 of the flowchart shown in FIG. 5, and themanagement-information memory status of the A system is changed to“Being copied” before the management-information copy process is startedat the step S505 of the flowchart shown in FIG. 5. The copy source ofthe management-information copy process is the B management-informationmemory switch 6. This copy source agrees with the Normalmanagement-information memory status of the B system and the “Accessesto management information in the management-information switch”management-information memory controller status 342 of the B system. Onthe other hand, the copy destination of the management-information copyprocess is the A management-information memory 32. This copy destinationagrees with the “Being copied” management-information memory status ofthe A system and results of the management-information copy process 341will reflect the fact that the management-information memory controllerstatus 342 of the A system has been changed to “Accesses to managementinformation in the storage controller.” Thus, management information iscopied from the B management-information memory switch 6 to the Amanagement-information memory 32 at the step S603 of the flowchart shownin FIG. 6.

As the copy operation is completed, the management-information memorystatus of the A system is restored to “Normal” at the step S606 of theflowchart shown in FIG. 6 while the management-information memory statusof the B system is changed to “Blocked” at the step S508 of theflowchart shown in FIG. 5 as shown in FIG. 9(c).

Then, the management-information memory controller status 342 of the Bsystem is changed to “Accesses to management information in the storagecontroller” at the step S511 of the flowchart shown in FIG. 5, and themanagement-information memory status of the B system is changed to“Being copied” before a second copy operation is started at the stepS512 of the flowchart shown in FIG. 5. The copy source of the secondcopy operation is the A management-information memory 32. This copysource agrees with the Normal management-information memory status ofthe A system and the “Accesses to management information in the storagecontroller” management-information memory controller status 342 of the Asystem. On the other hand, the copy destination of themanagement-information copy process is the B management-informationmemory 32. This copy destination agrees the “Being copied”management-information memory status of the B system and results of themanagement-information copy process 341 will reflect the fact that themanagement-information memory controller status of the B system has beenchanged to “Accesses to management information in the storagecontroller.” Thus, management information is copied from the Amanagement-information memory 32 to the B management-information memory32 at the step S603 of the flowchart shown in FIG. 6.

As this second copy operation is completed, the management-informationmemory status of the B system is restored to “Normal” at the step S606of the flowchart shown in FIG. 6 as shown in FIG. 9(d). In the stateshown in FIG. 9(d), the storage controller 3 is capable of operating bymaking accesses to management information stored in themanagement-information memory 32 having a duplicated-componentconfiguration.

Second Embodiment

Next, a second embodiment of the present invention is explained byreferring to FIGS. 10 to 14.

In this embodiment, the explanation of things common to the firstembodiment is not repeated. Instead, the second embodiment is explainedby focusing on technological differences from the first embodiment.

(I): Configuration of the Storage System

First of all, the configuration of the storage system 2 implemented bythe second embodiment is explained by referring to FIGS. 10 and 11. FIG.10 is a diagram showing the configuration of a storage system includingonly one storage controller 3 as implemented by the second embodiment ofthe present invention. On the other hand, FIG. 11 is a diagram showingthe configuration of a storage system including a plurality of storagecontrollers 3 as implemented by the second embodiment of the presentinvention.

In the case of the first embodiment, the storage controller 3 as well asthe management-information-memory switch 6 each have aduplicated-component configuration comprising 2 identical componentsand, when management information is copied from the storage controller 3to the management-information-memory switch 6 or vice versa, one of the2 identical components in the storage controller 3 and the counterpartof the 2 identical components in the management-information-memoryswitch 6 are put in Blocked status. Thus, in the course of amanagement-information copy process, the storage system 2 is capable ofcarrying out an operation without an interruption by using managementinformation stored in an unblocked component. In consequence, thestorage system 2 entails redundancy of the duplicated-componentconfigurations of the storage controller 3 and themanagement-information-memory switch 6.

The storage system 2 implemented by this embodiment is capable ofcarrying out an operation without an interruption even without entailingthe duplicated-component configurations of the storage controller 3 andthe management-information-memory switch 6.

In the case of a storage system 2 including only one storage controller3 as implemented by the second embodiment shown in FIG. 10, the storagesystem 2 is different from the first embodiment shown in FIG. 1 in that,in the case of the storage system 2 shown in FIG. 10, themanagement-information copy function 346 is carried out not by thechannel interface 31, but by management-information memory controller323 employed in the storage controller 3, and themanagement-information-memory status 344 is replaced bymanagement-information copy information 347. The management-informationcopy information 347 is information including a copy direction andmanagement-information memory status. The management-information copyinformation 347 can have 3 values, namely, “Copying managementinformation from storage controller to management-information memoryswitch”, “Copying management information from management-informationmemory switch to storage controller” and “Cleared”. The Clear valuemeans that no management-information copy function 346 is being carriedout.

In the case of a storage system 2 including a plurality of storagecontrollers 3 as implemented by the second embodiment shown in FIG. 11,on the other hand, the storage system 2 is different from the firstembodiment shown in FIG. 2 in that, in the case of the storage system 2shown in FIG. 11, the management-information copy function 346 iscarried out not by the channel interface 31, but bymanagement-information memory controller 323 employed in the storagecontroller 3, the management-information-memory status 344 is replacedby management-information copy information 347 and themanagement-information-memory switch 6 has management-information copyinformation 348 which has always the same value as themanagement-information copy information 347.

It should be noted that, even though FIGS. 10 and 11 show the storagecontroller 3 as well as the management-information-memory switch 6 eachhaving a duplicated-component configuration comprising 2 identicalcomponents as is the case of the first embodiment, theduplicated-component configurations may not necessarily be utilized inmanagement-information copy function 346.

(II): Procedures for Changing the Configuration of the Storage System

A procedure for changing the configuration of the storage systemimplemented by the second embodiment is the same as that of the firstembodiment explained earlier by referring to FIGS. 3 and 4. To be morespecific, a procedure for adding new storage controllers 3 and new discstorages 4 to the storage system 2 is the same as that represented bythe flowchart shown in FIG. 3. On the other hand, a procedure forremoving storage controllers 3 and disc storages 4 from the storagesystem 2 is the same as that represented by the flowchart shown in FIG.4.

(III): Details of Management-Information Copy Process and Process toAccess Management Information

The following description explains detailed procedures of a process tocopy management information and a process to make an access tomanagement information by referring to flowcharts shown in FIGS. 12 to14. FIG. 12 is a flowchart representing a procedure for copyingmanagement information when installing or removing storage controllers 3and disc storages 4 in or from the storage system 2. FIG. 13 is aflowchart representing a management-information copy function 346carried out in the storage controller 3. FIG. 14 is a flowchartrepresenting a procedure followed by the channel interface 31 and a discinterface 35 for making an access to management information.

The flowchart shown in FIG. 12 begins with a step S1001 at which theuser enters a copy direction to management-information memory controller323 employed in the storage controller 3 and activates themanagement-information copy function 346 via the service terminal 5. Tobe more specific, the user enters such a copy direction to the storagecontroller 3 so that, when the management-information-memory switch 6 isnewly installed in the storage system 2, management information iscopied from the storage controller 3 to themanagement-information-memory switch 6 and, when themanagement-information-memory switch 6 is removed from the storagesystem 2, on the other hand, management information is copied from themanagement-information-memory switch 6 to the storage controller 3.

Then, at the next step S1002, the storage system 2 enters a state ofwaiting for completion of the management-information copy function 346carried out by management-information memory controller 323 employed inthe storage controller 3.

Next, the management-information copy function 346 is explained byreferring to a flowchart shown in FIG. 13. As shown in the figure, theflowchart begins with a step S1101 at which acopied-management-information address 343 is set to point to thebeginning of the copy destination of management information. Then, theflow of the process goes on to a step S1102 to determine whether thedirection of the process to copy management information is from thestorage controller 3 to the management-information-memory switch 6. Ifthe direction of the process to copy management information is from thestorage controller 3 to the management-information-memory switch 6, theflow of the process goes on to a step S1103 at which themanagement-information copy information 348 of themanagement-information-memory switch 6 is changed to “Copying managementinformation from the storage controller to themanagement-information-memory switch.” Then, at the next step S1104, themanagement-information copy information 347 of the storage controller 3is changed to “Copying management information from the storagecontroller to the management-information-memory switch.”

If the direction of the process to copy management information is fromthe management-information-memory switch 6 to the storage controller 3,on the other hand, the flow of the process goes on to a step S1105 atwhich the management-information copy information 348 of themanagement-information-memory switch 6 is changed to “Copying managementinformation from the management-information-memory switch to the storagecontroller.” Then, at the next step S1106, the management-informationcopy information 347 of the storage controller 3 is changed to “Copyingmanagement information from the management-information-memory switch tothe storage controller.”

Then, the flow of the process goes on to a step S1107 to determinewhether the address 343 of copied management information has reached theend of the management-information copy destination. If the address 343of copied management information has reached the end of themanagement-information copy destination, the flow of the process goes onto a step S1111. If the address 343 of copied management information hasnot reached the end of the management-information copy destination, onthe other hand, the flow of the process goes on to a step S1108 at whichmanagement information of a predetermined amount is copied from thecontroller-internal management-information memory module 321 or theswitch-internal management-information memory module 62 serving as acopy source to respectively the switch-internal management-informationmemory module 62 or the controller-internal management-informationmemory module 321 serving as the copy destination.

Subsequently, the flow of the process goes on to a S1109 at which theaddress 343 of copied management information is updated. Then, at thenext step S1110, the management-information copy function 346 issuspended for a predetermined period of time in order to prevent anaccess request made by the channel interface 31 or the disc interface 35from being kept waiting for a long period of time. After a predeterminedperiod of time has lapsed, the flow of the process goes back to the stepS1107.

At the step S1111, the management-information copy information 347 ofthe storage controller 3 is cleared. Subsequently, at the next stepS1112, the management-information copy information 348 of themanagement-information-memory switch 6 is cleared.

The flow of the process then goes on to a step S1113 to determinewhether the direction of the process to copy management information isfrom the storage controller 3 to the management-information-memoryswitch 6. If the direction of the process to copy management informationis from the storage controller 3 to the management-information-memoryswitch 6, the flow of the process goes on to a step S1114 at which themanagement-information memory controller status 342 is changed to“Accesses to management information in the management-information-memoryswitch.” If the direction of the process to copy management informationis from the management-information-memory switch 6 to the storagecontroller 3, on the other hand, the flow of the process goes on to astep S1115 at which the management-information memory controller status342 is changed to “Accesses to management information in the storagecontroller.”

The management-information-memory-controller status 342 indicateswhether the storage controller 3 should make an access to managementinformation stored in the storage controller 3 or themanagement-information-memory switch 6. Thus, after themanagement-information copy function 346 is completed, the storagecontroller 3 always makes accesses to management information stored inthe copy destination.

FIG. 14 is a flowchart representing a procedure followed by the channelinterface 31 and a disc interface 35 for making an access to managementinformation.

As shown in the figure, the flowchart begins with a step S1201 todetermine whether the management-information memory controller status342 is “Accesses to management information in the storage controller.”If the management-information memory controller status 342 is “Accessesto management information in the storage controller,” the flow of theprocedure goes on to a step S1202 to make a request for an access tomanagement information in the controller-internal management-informationmemory module 321 . If the management-information memory controllerstatus 342 is “Accesses to management information in themanagement-information-memory switch,” on the other hand, the flow ofthe procedure goes on to a step S1203 to make a request for an access tomanagement information in the switch-internal management-informationmemory module 62.

The flow of the procedure then goes on to a step S1204 to determinewhether the management-information copy information 347 has beencleared. If the management-information copy information 347 has beencleared, the processing to handle the request for an access is ended.This is because cleared management-information copy information 347indicates that no management-information copy process is being carriedout so that only normal processing needs to be carried out. On the otherhand, uncleared management-information copy information 347 indicatesthat a management-information copy process is being carried out with theaccess target serving as a copy source. In this case, the flow of theprocedure goes on to a step S1205 at which the copiedmanagement-information address 343 is referenced. The flow of theprocedure then goes on to a step S1206 to determine whether the accessrequest is a write request and whether the address of the access targetlies ahead of the address 343 of copied management information. Anaddress of the access target lying ahead of the address 343 of copiedmanagement information indicates that the access is an access to aregion for which a copy operation has already been completed. This isbecause a copy operation starts from a start address toward subsequentaddresses.

If at least the access request is not a write request or the address ofthe access target does not lie ahead of the address 343 of copiedmanagement information, the processing to handle the request for anaccess is ended. Such an access request is a read request or a requestto write data into an area for which a copy operation has not beencompleted. For such a write request, the data is merely written into thecopy source.

Then, the flow of the procedure goes on to a step S1207 to determinewhether the management-information memory controller status 342 is“Accesses to management information in the storage controller.” If themanagement-information memory controller status 342 is found to be“Accesses to management information in the storage controller,” the flowof the procedure goes on to a step S1208 at which data is alsooverwritten into management information of the switch-internalmanagement-information memory module 62 through themanagement-information-memory switch 6. If the management-informationmemory controller status 342 is found to be “Accesses to managementinformation in the management-information-memory switch,” on the otherhand, the flow of the procedure goes on to a step S1209 at which data isalso overwritten into management information of the controller-internalmanagement-information memory module 321.

That is, if the access request is a write request and the address of theaccess target lies ahead of the address 343 of copied managementinformation, the data is written into an area for which the copyoperation has been completed. In this case, the data is also writtenover management information of the copy source to maintain integrity ofmanagement information after completion of the management-informationcopy process.

Invention's Effects Revealed by the Embodiments

As is obvious from the description of the embodiments, the presentinvention allows the configuration of a storage system to be changedwith ease. Even in the case of a storage system comprising a pluralityof system components integrated into an integrated storage system, theintegrated storage system can be managed logically as a single storagesystem wherein the storage locations of management information can beselected in accordance with the configuration of the storage system sothat it is possible to execute centralized management of managementinformation without regard to the configuration, allowing a storagesystem free of deterioration of performance of making accesses tomanagement information to be provided.

In addition, in accordance with the present invention, there is alsoprovided a method for configuring a storage system which allows a hostto make accesses to a disc storage of the storage system withoutsuspending the operation of the storage system even while theconfiguration of the storage system is being changed.

What is claimed is:
 1. A storage system (allowing a host computer tomake accesses to disc storages and) comprising one or more storagecontrollers and storages, and allowing a host computer to make accessesto said storages without suspending the operation of the storage systemeven while the configuration of the storage system is being changed byadding or removing a storage controller from the said storage system,wherein: each of said storage controllers includes: a channel interfaceconnected to said host computer; an interface connected to saidstorages; and a management-information memory for storing managementinformation of said storage system; wherein if said storage systemincludes a plurality of said storage controllers, then saidmanagement-information memories employed in said storage controllers areconnected to each other by a management-information-memory switch havinga switch-internal management-information memory module; if said storagesystem includes only one said storage controller, then saidmanagement-information memory of said storage controller has acontroller-internal management-information memory controller and acontroller-internal management-information memory module; if saidstorage system includes a plurality of said storage controllers, thensaid management-information memories employed in said storagecontrollers each have said controller-internal management-informationmemory controller; if said storage system includes only one said storagecontroller, then said controller-internal management-information memorycontroller makes an access to said controller-internalmanagement-information memory module inside said storage controller; andif said storage system includes a plurality of said storage controllers,then said controller-internal management-information memory controllersmake accesses to said switch-internal management-information memorymodule inside said management-information-memory switch.
 2. A storagesystem according to claim 1, wherein, if said storage system includesonly one of said storage controllers, then management information isstored in said controller-internal management-information memory moduleinside said storage controller and, if said storage system includes aplurality of said storage controllers, then management information isstored in said switch-internal management-information memory moduleinside said management-information-memory switch.
 3. A method ofconfiguring a storage system comprising one or more storage controllersand storages and allowing a host computer to make accesses to saidstorages without suspending the operation of the storage system evenwhile the configuration of the storage system is being changed by addingor removing a storage controller from the said storage system, wherein:each of said storage controllers includes: a channel interface connectedto said host computer; an interface connected to said storages; and amanagement-information memory for storing management information of saidstorage system; if said storage system includes only one said storagecontroller, then said management-information memory of said storagecontroller has a controller-internal management-information memorycontroller and a controller-internal management-information memorymodule; and if said storage system includes a plurality of said storagecontrollers, then said management-information memories employed in saidstorage controllers are connected to each other by amanagement-information-memory switch having a switch-internalmanagement-information memory module and said management-informationmemories employed in said storage controllers each have saidcontroller-internal management-information memory controller.
 4. Amethod of configuring a storage system in accordance with claim 3,wherein, if said storage system includes only one of said storagecontrollers, then management information is stored in saidcontroller-internal management-information memory module inside saidstorage controller and, if said storage system includes a plurality ofsaid storage controllers, then management information is stored in saidswitch-internal management-information memory module inside saidmanagement-information-memory switch.
 5. A method of configuring astorage system in accordance with claim 3, wherein saidmanagement-information memories employed in each of said additionalstorage controllers and said management-information-memory switchesconsist of duplicated-management-information-storing systems whereby,when some of said storage controllers are newly installed in addition toonly one of said storage controllers already existing in said storagesystem: said management-information-memory switches are newly added forconnecting said management-information memories employed in said storagecontrollers to each other; for each of saidduplicated-management-information-storing systems, saidmanagement-information memory is connected to saidmanagement-information-memory switch; to change stored locations ofmanagement information from said management-information memories of saidstorage controller already existing in said storage system to saidmanagement-information-memory switches, saidduplicated-management-information-storing systems are sequentiallysubjected one system after another to a procedure comprising the stepsof: blocking one of said duplicated-management-information-storingsystems; copying management information of the unblocked one ofduplicated-management-information-storing systems from saidmanagement-information memory to said management-information-memoryswitch of said blocked duplicated-management-information-storing system;and de-blocking said blocked duplicated-management-information-storingsystem; and said storage system carries out processing of an access madeby said host computer to said storages while said stored locations arebeing changed by using management information stored in an unblocked oneof said duplicated-management-information-storing systems.
 6. A methodof configuring a storage system in accordance with claim 3, wherein saidmanagement-information memories employed in each of said additionalstorage controllers and said management-information-memory switchesconsist of duplicated-management-information-storing systems whereby,when some of said storage controllers are removed from said storagesystems to leave only one of said storage controllers in said storagesystem with said management-information memories connected to saidmanagement-information-memory switch in all saidduplicated-management-information storing systems, to change storedlocations of management information from saidmanagement-information-memory switches to said management-informationmemories of said storage controller to leave alone in said storagesystem, said duplicated-management-information-storing systems aresequentially subjected one system after another to a procedurecomprising the steps of: blocking any one of saidduplicated-management-information-storing systems; copying managementinformation of the unblocked one of saidduplicated-management-information-storing systems from saidmanagement-information-memory switch to said management-informationmemory of said blocked duplicated-management-information-storing system;and de-blocking said blocked duplicated-management-information-storingsystem, and said storage system carries out processing of an access madeby said host computer to said storages while said stored locations arebeing changed by using management information stored in an unblocked oneof said duplicated-management-information-storing systems.
 7. A methodof configuring a storage system in accordance with claim 3, whereby,when some of said storage controllers are newly installed in addition toonly one of said storage controllers already existing in said storagesystem: said management-information-memory switch is newly added forconnecting said management-information memories employed in said storagecontrollers to each other; and to change stored locations of managementinformation from said management-information memory employed in saidstorage controller already existing in said storage system to saidmanagement-information-memory switch, management information stored insaid management-information memory is copied to saidmanagement-information-memory switch in a copy operation; and saidstorage system carries out processing of an access made by said hostcomputer to said storages while said stored locations are being changedby using management information stored in said management-informationmemory employed in said storage controllers each serving as a source ofsaid copy operation.
 8. A method of configuring a storage system inaccordance with claim 3, whereby, when some of said storage controllersare removed from said storage systems to leave only one of said storagecontrollers in said storage system with said management-informationmemories connected to said management-information-memory switch: tochange stored locations of management information from saidmanagement-information-memory switch to saidmanagement-information-memory of said storage controller to leave alonein said storage system, management information stored in saidmanagement-information-memory switch is copied to saidmanagement-information-memory in a copy operation; and said storagesystem carries out processing of an access made by said host computer tosaid storages while said stored locations are being changed by usingmanagement information stored in said management-information-memoryswitch serving as a source of said copy operation.